Growing plants on an inert medium as mechanical support provided with other components such as seeds, nutrients, and the like is known in the art. In some instances, the mechanical support is in the form of loose particulate material such as peat, vermiculite, perlite, fly ash, pumice, rock wool, glass wool, organic and inorganic fibres or particles, and the like. The problem with these materials, sometimes admixed with soil, is that they can be washed away rather easily with running water and wind (cf. e.g., JP2004229637, US2004132869). Alternatively, the inert support can be in the form of a self supported material in the form of slabs, block, or mats of various rigidities and thicknesses (cf. e.g., U.S. Pat. No. 3,877,172). The same materials as listed above can be used in such forms of support and, since said self supported materials must be permeable to water, the use of foams with open porosity of controlled dimension has been proposed quite advantageously. Apart from the enhanced stability of such foams compared with support in particulate form, foams can be used to dress steep slopes and even vertical walls without any problem. In order to manage the water balance within the foam, foam supports must be provided with a drainage system. The control of water drainage is very important. Indeed, if the drainage is insufficient, water will saturate the structure and stagnate around the roots. On the other hand, water would just wash through the material in case of excessive drainage, thus depleting the roots from water when needed.
For example, U.S. Pat. No. 4,023,308 discloses a foraminous support body to be placed in the bottom of the container and prior to the time it is placed therein, it is perforated to form cylindrical conduits vertically completely through the foraminous body wherein the perforations are about 1-5 mm in diameter and are spaced apart about 1-8 mm. This solution allows to control the permeability of the support slab, but not to retain any water therein. It therefore does not permit to manage the water balance within the support material.
JP2002084889 proposes a plate-like, water-retaining pad for greening rooftops comprising the solidified product of fibres with a foamed polyurethane and compression-moulding longitudinal and latitudinal grooves on the back side of the pad.
DE10008021 discloses a water retaining and draining pad comprising bonded rubbery granules, covered by a fleece or felt layer. The covering as a whole is both waterproof and stores water. Granularity and production are controlled, to assure adequate water retention and permeability.
US 2007186467 proposes a foamed glass plant growth support structure, including a foamed glass substrate and a plurality of interconnected pores distributed throughout the substrate. The substrate is characterized by a porosity of at least about 80 percent. The pore size is substantially between about 0.2 and about 5 millimeters and the substrate is sufficiently chemically stable such that water filling the plurality of interconnected pores experiences a pH shift of less than 0.5.
WO94/03045 discloses a mineral wool shaped body provided with a water barrier or water permeability inhibiting coating layer made of argillaceous materials, clays or their artificial mixtures applied on the bottom surface and side surfaces of the body, so that a water storage is formed inside the body.
All the above products offer a solution to control the water percolation through a porous structure, and some of them teach how to evacuate water with draining grooves, but none offers a global water management solution, wherein excess water is drained out of the foam to avoid stagnation, but wherein a controlled amount of water is nonetheless stored, to maintain a constant level of moisture, thus acting as a water buffer. The present invention proposes a solution to this and to other problems as will appear clearly from the following description of the invention. In particular, supports can be inert or be provided with a plant growth promoting functionality by incorporating within the porous support material additives such as fertilizers, plant nutrients, and pesticides. The present invention proposes a solution how to incorporate such additives within the support.